The invention relates generally to thermal inspection systems and methods and more specifically, to non-destructive thermal inspection for internal cavities in a part.
There are several techniques that are currently used for inspection of parts for internal cavities. A commonly used technique is “flow checks”. A flow check measures a total flow through a part. Blockage of various film holes or rows of holes, or entire flow circuits or passages, provides measurements for the remaining holes or groups of holes, or flow circuits. The process is repeated with various holes or passages blocked until all desired measurements have been made. Comparisons to either gauge measurements on reliable parts and analytical models of flow circuits determines the acceptability of the parts. However, the technique is known to be time consuming resulting in a check of only selective film holes, groups of holes, or flow circuits. Additionally, the technique has the propensity to overlook local or individual features or holes that are out of specification.
Other techniques include dimensional gauges, for example pin checks, and other visual methods, for example water flow. Industry typically relies on these methods to determine the quality of each part as compared to a nominal standard part or a specification. However, such dimensional or visual techniques do not lend themselves to distinguishing between two parts that may have very different thermal-flow performance, but which flow the same amount and otherwise pass all external dimensional and visual tests.
Pulsed thermography is a surface inspection technique in which a thermal pulse (or flash) is applied to a part, and the thermal response of the surface of part is then detected. However, thermal saturation is not achieved with pulsed thermography due to the limited time duration and penetration of the part. Accordingly, the global thermal conduction response for the part cannot be determined using pulsed thermography, due to the limited thermal penetration depth of that method.
Accordingly, there is a need for an improved method of thermal inspection and specifically, there is a need for a quantitative, non-destructive thermal inspection system and method. In particular, there is a need for a thermal inspection technique that determines the global, thermal response of a part.